More than three-quarters of the wetlands in southeastern New Jersey is saltwater tidal marshes, which provide a critical habitat for commercially important species of fish and crabs, as well as for birds such as ospreys and bald eagles.

Without these marshes, the water quality in area back bays and nearby beaches would suffer, and the amount of crabs, flounder and other locally harvested seafood would be significantly less, if not gone all together.

“The wetlands do a lot for the water quality and the ecology,” said Fred Akers, director of the Great Egg Harbor Watershed Association and a wetlands advocate, as his feet sloshed through the rising tide on a marshy island near the mouth of English Creek. “I think the key ingredient of the wetlands is the vegetation that becomes the bottom of the food chain. Everything else that lives here relies on it. The salt hay even uptakes (absorbs) the pollutants.”

Click here for video on life in the marsh

Research by Rutgers University scientist Judith Weis has found over the years that salt marsh grasses absorb heavy metals from contaminated soil and keep the pollutants in the plant’s stems, leaves and roots. The grasses, in effect, help clean the polluted soil, several of Weis’ research papers state.

Saltwater marshes are among the most highly regulated ecosystems in the state, falling under several laws, including the New Jersey State Coastal Area Facilities Review Act and the Wetlands Act of 1970. Both laws were passed out of concern that development would destroy the marshes, which also help absorb rising tidal floods due to storms.

Today, development regulations are so tight that the owner of a billboard along the Margate Causeway may be forced to move the structure’s pole 24 feet to avoid encroaching on the marsh, Department of Environmental Protection documents indicate.

Staffers and volunteers with the DEP and area environmental advocacy groups closely monitor the health of the life and water in the salt marshes, taking water samples, counting birds and compiling other data for researchers.

The vast, flat grasslands are teeming with life. In just about a quarter-acre of the marsh off Jeffers Landing Road in the Scullville section of Egg Harbor Townhip, tiny purple fiddler crabs stand on muddy banks, waving their one large claw in the air; black mud snails leave curly trails in the shallow muck; tiny silverfish trapped in inch-deep pools nestle in the middle of the grass; and large blue crabs are nearly obscured by the mud they’ve buried themselves in during low tide.

Then there are the dozens of species of birds that fly in for lunch and leave, or roost and nest, raising their young off the plentiful food.

When explorers arrived in South Jersey, they were so taken by the number of birds nesting in the salt meadows along the water that they called the river the Great Egg Harbor, said Akers, who teaches residents about environmental issues and the river’s history. Although hunting and, ultimately, DDT and other pollutants decimated the avian populations, the birds — including ospreys, eagles, egrets and herons — are returning, according to recent wildlife surveys done by the DEP and area environmental advocacy groups.

Wetlands, which include tidal salt marshes and nontidal freshwater swamps, cover more than 300,000 acres in southeastern New Jersey, the largest concentration in the state. Those wetlands, particularly the salt marshes, provide a critical habitat for commercially important species and act as a water filter that cleans and improves the quality of the region’s bays and beaches.

Below the surface of the pungent-smelling muck are worms and clams. At the surface are massive clumps of black-ribbed mussels. In the nearby deeper water, dozens of fish species, plus shrimp, crabs and turtles, swim or move about along the muddy bay floor.

The wetlands change several times a day as the pulse of the tide ebbs and flows, swelling with water about every 13 hours. At low tide, wading birds, such as egrets and herons, feed along the exposed muddy flats, looking for tiny fish trapped by the receded tide. But as the water rises again, the birds find their food closer to or even in the grasses.

At low tide, the large masses of ribbed mussels are exposed. Their shells are clamped shut to keep in moisture. The bivalves, which are a different species than those typically found in the ocean and on restaurant menus, are so prolific along the banks of the marsh that they actually help stabilize the muck.

But when the water rises, the mussels’ shells open slightly so that they can feed by filtering water over their gills.

The marsh is an environment in which every inch of height counts. Tiny differences in topography determine which plant species will live where and whether an area will stay flooded, or flood only at an extreme high tide, or even whether an area will become covered with trees and bushes.

As the tide gradually comes in, the creatures that were dormant in the mud begin to move. Blue crabs come out, snails start moving about and tiny fish left in shallow pools have more water as the pool expands.

When the water is very high — as it is when the moon is new or full — crabs and fish will swim between the blades of grass, searching for food, whether that is plant life or smaller fish and crabs. Those forages into the grass, in turn, will draw the birds, searching for food.

More than half of Cape May County is considered wetlands, with the vast majority of that tidal marsh. Most of Cumberland County’s 110,000 wetland acres are also tidal marsh, as is more than three quarters of Atlantic County’s 132,000 acres of wetlands.

The Environmental Law Institute reported in its August 2011 National Wetlands Newsletter that policymakers and scientists are looking at whether restoring tidal wetlands could help mitigate climate change due to the grasses’ role in sequestering carbon dioxide in the soil, helping reduce the amount of excess greenhouse gases in the atmosphere. Conversely, as wetlands are destroyed, methane that forms from decomposing plant life is released. Methane is a greenhouse gas that is a more potent heat trapper than carbon dioxide.

Years ago, Akers said, the salt meadows were farmed. They provided pasture land for livestock, or the grass was harvested for packing material for the region’s glass factories. Horses were fitted with special shoes to keep their legs from sinking into the muck, and cattle roamed closer to the landward edges, where the ground is firmer than it is by the water.